"E-cigarettes are at least 95 per cent less harmful than tobacco smoking, and they are now the most popular aid to quitting smoking in the UK," Dr Notley said.

"However the idea of using e-cigarettes to stop smoking, and particularly long-term use, remains controversial.

"We found that vaping may support long-term smoking abstinence.

"Not only does it substitute many of the physical, psychological, social and cultural elements of cigarette smoking, but it is pleasurable in its own right, as well as convenient and cheaper than smoking.

"But the really interesting thing we found was that vaping may also encourage people who don't even want to stop smoking, to eventually quit."

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Alison Cox, director of cancer prevention at Cancer Research UK, which helped fund the study, said: "The evidence so far shows that e-cigarettes are far safer than tobacco.

"E-cigarettes do still contain nicotine which is addictive, but it's not responsible for the major harms of smoking.

"It's great to see this early indication that e-cigarettes could encourage smokers who weren't originally thinking of quitting to give up.

"But more research is needed to understand exactly how e-cigarettes are being used by people who don't want to stop smoking and how often this results in quitting."

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